Total Synthesis and Configurational Assignment of Ascospiroketal A.

The total synthesis of the marine fungus-derived natural product ascospiroketal is described. This concise synthesis relies on a unique Ag(I) -promoted tandem cascade cyclization that provides direct access to the correctly configured tricyclic core of the natural product from a linear precursor. The synthesis of candidate stereostructures of ascospiroketal A allowed for the confident assignment of both the relative and absolute stereochemistry of this unusual octaketide.